The mainstream of the modern semiconductor industry involves resin encapsulated diodes, transistors, IC, LSI, and super LSI. Among various resin compounds for encapsulating semiconductor devices, epoxy resin compositions comprising curable epoxy resins blended with curing agents and various additives are most widely used because they are generally improved in moldability, adhesion, electrical properties, mechanical properties and moisture resistance over the rest of thermosetting resins. The present day trend for these semiconductor devices is toward an increasingly high degree of integration and increased chip size therewith. Packages, on the other hand, are desired to be smaller and thinner in outer dimensions to meet the demands of compactness and light weight for electronic equipment. Further, as to the attachment of semiconductor parts on circuit boards, surface mounting of semiconductor parts is now often employed for reasons of increased part density on boards and reduced board thickness.
A common approach to the surface mounting of semiconductor parts is to dip entire semiconductor devices in a solder bath or to pass them through a hot zone of molten solder. Thermal shocks associated with this process cause encapsulating resin layers to crack or incur separation at the interface between the lead frames or chips and the encapsulating resin. Such cracks and separation become more outstanding if the semiconductor device encapsulating resin layers have absorbed moisture prior to thermal shocks encountered during surface mounting. Since encapsulating resin layers, however, inevitably absorb moisture in practical manufacturing steps, epoxy resin-encapsulated semiconductor devices after mounting sometimes suffer from a loss of reliability.